The oncogenic function of PLAGL2 is mediated via ASCL2 and IGF2 and a Wnt-independent mechanism in colorectal cancer

Abstract

Colorectal cancer (CRC) tumorigenesis and progression are linked to common oncogenic mutations, especially in the tumor suppressor APC, whose loss triggers the deregulation of TCF4/β-Catenin activity. CRC tumorigenesis is also driven by multiple epi-mutational modifiers, such as transcriptional regulators. We describe the common (and near-universal) activation of the zinc finger transcription factor and Let-7 target PLAGL2 in CRC and find that it is a key driver of intestinal epithelial transformation. PLAGL2 drives proliferation, cell cycle progression, and anchorage-independent growth in CRC cell lines and non-transformed intestinal cells. Investigating effects of PLAGL2 on downstream pathways revealed very modest effects on canonical Wnt signaling. Alternatively, we find pronounced effects on the direct PLAGL2 target genes IGF2, a fetal growth factor, and ASCL2, an intestinal stem cell-specific bHLH transcription factor. Inactivation of PLAGL2 in CRC cell lines has pronounced effects on ASCL2 reporter activity. Furthermore, ASCL2 expression can partially rescue deficits of proliferation and cell cycle progression caused by depletion of PLAGL2 in CRC cell lines. Thus, the oncogenic effects of PLAGL2 appear to be mediated via core stem cell and onco-fetal pathways, with minimal effects on downstream Wnt signaling.

An imbalance between proliferation and differentiation underlies the development of microRNA-defective pineoblastoma

“…Outside the brain, PLAGL2 also contributes to oncogenesis in lung cancer [77,78], colorectal cancer [79][80][81][82], gastric cancer [83], breast cancer [84,85], and acute myeloid leukemia [86]. In these cancers, PLAGL2 has been shown to contribute to proliferation, epithelial-mesenchymal transition, and "stemness" by regulating target genes such as Igf2 and regulators of Wnt signaling [73,76,79,80,82,85]. To our knowledge, however, this is the first description of PLAGL2 upregulation in DROSHA-or DICER1-related pediatric cancers.…”

“…In the embryonic brain and in brain tumors, Plagl2 regulates the balance between differentiation and proliferation, and its overexpression shifts neural progenitors towards proliferation [75, 76]. Outside the brain, PLAGL2 also contributes to oncogenesis in lung cancer [77, 78], colorectal cancer [79–82], gastric cancer [83], breast cancer [84, 85], and acute myeloid leukemia [86]. In these cancers, PLAGL2 has been shown to contribute to proliferation, epithelial-mesenchymal transition, and “stemness” by regulating target genes such as Igf2 and regulators of Wnt signaling [73, 76, 79, 80, 82, 85].…”